SKY & TELESCOPE'S NEWS BULLETIN -- JULY 15, 1994

THE COMET COMETH

After a year of anticipation, Periodic Comet Shoemaker Levy 9 is about to
put on a grand show, and the world's astronomers are watching. The
comet's 20 known fragments will strike the southern hemisphere of Jupiter
on the dark side just out of view of Earth, beginning July 16th. The
following times are calculated from positional data gathered through July
11th, with a July 15th adjustment for fragment A; a more detailed update
is expected just a few hours before the first impact. The values include
the 42.5 minutes of light time between Jupiter and the Earth and are given
in Pacific Daylight time. However, positional uncertainties are still
fairly large, and these times are only good to plus or minus 15 minutes in
most cases.

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The impacts of fragments B, F, R, and V are the only ones that occur when
Jupiter is viewable from North America. Even though the impacts
themselves occur on Jupiter's back side, the target zones will rotate into
view along the planet's southeast limb no more than 20 minutes later.

Unfortunately Jupiter will be observable well for only an hour or two out
of every 24 from any given location at north temperate latitudes. It's the
bright "star" fairly high in the southwest as darkness falls. The cover
story of the July Sky & Telescope provides full coverage of this event and
how to try to watch.

A new analysis of Hubble Space Telescope images suggests that the impacts
could be impressive. Zdenek Sekanina reports that not only do the biggest
nuclei appear to be 3 to 4 kilometers across, but some of them may have
split off smaller clumps as they have neared the planet.

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